The present invention relates to an engine control apparatus for simultaneously controlling a plurality of cylinders of an internal combustion engine on the basis of a plurality of cylinder-group identifying signals. More particularly, it relates to such an engine control apparatus which can utilize a simple and inexpensive control unit in the form of a microcomputer.
A typical example of such an engine control apparatus is illustrated in FIG. 5. The apparatus illustrated is to control a multi-cylinder engine having six cylinders which are grouped into three paris. In FIG. 5, the engine includes a crankshaft 1 which performs two revolutions per engine cycle for each cylinder including an intake stroke, a compression stroke, a combustion stroke and an exhaust stroke. An arcuate-shaped reference position indicating member 2, which is formed, for example, from a magnetic material, is mounted on the crankshaft 1 and has a forward or leading end 2a and a rearward or trailing end 2b corresponding, respectively, to two crank angle reference positions. A plurality (three in the illustrated example) of reference position sensors 3 each comprising an electromagnetic pickup are disposed around the outer peripheral surface of the crankshaft 1 at equal circumferential intervals (e.g., at an angle of 120 degrees in the illustrated example) in such a manner that they can be placed in a face-to-face relation with respect to the reference position indicating member 2 during the rotation of the crankshaft 1. Thus, each of the sensors 3 generates an output signal in the form of a cylinder-group identifying signal S1, S2 or S3 each time it faces the reference position indicating member 2 during rotation thereof, as shown in FIG. 6.
A controller 4 generates, based on the cylinder-group identifying signals S1 through S3, control signals comprising an ignition signal E and a fuel injection signal F for corresponding groups of cylinders. The controller 4 includes a control unit in the form of a microcomputer 41 having a plurality of interrupt terminals INT1 through INT3 to which cylinder-group identifying signals S1 through S3 from the corresponding reference position sensors 3 are respectively input, and an output interface 42 from which the ignition signal E and the fuel injection signal F generated by the microcomputer 41 are output to an ignition coil 5 and an injection coil 6.
The ignition coil 5 includes a primary winding 5a and a secondary winding 5b and generates a high voltage across the secondary winding 5b when an ignition signal E generated by the controller 4 is input to the primary winding 5a. When the controller 4 generates a fuel injection signal F, the injection coil 6 is energized to drive an unillustrated injector for injecting fuel to an unillustrated intake manifold of the engine.
Though not shown, each of the cylinders is provided with an intake valve and an exhaust valve which are driven to open and close through a valve operating mechanism in synchronization with the rotation with the crankshaft 1 for supplying an air/fuel mixture to each cylinder and discharging exhaust gases therefrom.
The operation of the above-described engine control apparatus will now be described below with particular reference to a waveform diagram of FIG. 6. As the engine starts to operate, the reference position sensors 3 generate cylinder-group identifying signals S1 through S3 each for a corresponding group of cylinders, respectively, in synchronization with the rotation of the crankshaft 1. As depicted in FIG. 5, each of the cylinder-group identifying signals S1 through S3 includes a pulse which rises when the corresponding reference position sensor 3 is placed in a face-to-face relation with the leading end 2a of the reference position indicating member 2 (i.e., at a first reference position A), and which falls when the corresponding reference position sensor 3 is placed in a face-to-face relation with the trailing end 2b of the reference position indicating member 2 (i.e., at a second reference position B). The first and second reference positions A and B can arbitrarily be set, for example, to a crank angle near a conduction or power supply starting timing of the ignition coil 5 and another crank angle near a conduction or power supply cut-off timing thereof, respectively.
Upon the rising of a pulse of the cylinder-group identifying signal S1, i.e., when an interrupt signal S1 is input to the interrupt terminal INT1 of the microcomputer 41, the microcomputer 41 initiates an interrupt processing whereby it generates an ignition signal E and a fuel injection panel F for a first group of two cylinders. At this time, one of the two cylinders to be controlled by these signals E, F is in the combustion stroke whereas the other cylinder is in the intake stroke, so only the one cylinder undergoing the combustion stroke is fired to perform combustion of a mixture therein whereas the other cylinder in the intake stroke remains unchanged upon firing, causing no combustion. Similarly, other groups (i.e., a second group and a third group) of cylinders are sequentially controlled in accordance with cylinder-group identifying signals S2, S3, respectively.
With the above-described engine control apparatus, however, the controller 4 including the microcomputer 41 having the plurality of interrupt terminals INT1 through INT3 corresponding to the plurality of cylinder-group identifying signals S1 through S3, respectively, is expensive, thus making it difficult to cut down the manufacturing costs.
Moreover, if one of the reference position sensors 3 fails during the operation of the engine, a corresponding one of the cylinder-group identifying signals S1 through S3 can no longer be provided. In this case, the controller 4 or the microcomputer 41 identifies, based on no input of an interrupt signal to a corresponding interrupt input terminal, a group of cylinders corresponding to the failed reference position sensor 3 and performs fail-safe control on this group of cylinders. For example, if a cylinder-group identifying signal S2 for the second group of cylinders is not provided, the controller 4 controls these cylinders on the basis of an interrupt signal in the form of a first cylinder-group identifying signal S1. In this case, however, there is a relatively long period of time from the time of generation of the first cylinder identification signal S1 until the time when the second group of cylinders are actually controlled, thus giving rise to a relatively large error or time lag in control timing. In other words, since the controller 4 generates control signals E and F based solely upon cylinder-group identifying signals S1 through S3 from the reference position sensors 3, it is difficult to backup a failure of any of the reference position sensors 3 is a reliable manner.